1. Field of the Invention
This invention relates to a lubricating oil composition having good antiwear and/or antioxidation performance due to the presence of an O-alkyl-N-alkoxy-carbonylthionocarbamate salt of dialkyldithiophosphoric acid.
2. Description of Related Art
Engine lubricating oils require the presence of additives to protect the engine from wear. For almost forty years, the principal antiwear additive for engine lubricating oils has been zinc dialkyldithiophosphate (ZDDP). Typically, ZDDP must be used in concentrations of about 1.0 to 1.4 wt.% or greater to be effective in reducing wear. However, phosphates may cause the deactivation of emission control catalysts used in automotive exhaust systems. In addition, ZDDP alone does not provide the enhanced antiwear protection necessary in oils used to lubricate today's small, high performance engines. Furthermore, ZDDP also adds to engine deposits which cause increased oil consumption and increased particulate and regulated gaseous emissions. Accordingly, reducing or eliminating the amount of phosphorus-containing additives (such as ZDDP) in the oil would be desirable.
O-alkyl-N-alkoxycarbonylthionocarbamates and their method of preparation are known (see U.S Pat. No. 4,659,853, the disclosure of which is incorporated herein by reference). In addition, copending patent application U.S. Ser. No. 805,757 filed on the same date herewith discloses that O-alkyl-N-alkoxycarbonyl-thionocarbamates impart improved antiwear and/or friction reducing performance to lubricating oils. However, neither the patent nor the application mention the use of O-alkyl-N-alkoxycarbonylthionocarbamate salts of dialkyldithiophosphoric acid in a lubricating oil.